Finding. During the ISS era, the orbiter will be unable to use some current operational techniques to improve its survivability in the face of meteoroids and orbital debris.

NASA has developed procedures to detect, locate, and repair small punctures in the orbiter crew cabin. However, no in-flight procedures have been developed to detect, locate, and repair punctures elsewhere on the vehicle. This capability could be very useful because many of the orbiter’s potential failure modes caused by meteoroid or debris impact may not be critical immediately but could become critical during reentry. If they could be detected and repaired in orbit, the risk of critical failure could be significantly reduced.

On most missions, significant damage from meteoroids and orbital debris could be located without an EVA. Large portions of the orbiter’s critical areas can be surveyed for impact damage with the remote manipulator system (RMS) cameras, if the RMS is on board (80 to 90 percent of planned missions). Figure 6–4 shows how the RMS could be used to survey the orbiter for damage. NASA is also considering stationing free-flying monitor robots at the ISS; these would be able to examine a shuttle docked at the station.

Repairing significant damage from meteoroids or orbital debris outside the pressurized area might also be feasible although it would require at least one EVA. Before the first shuttle flight, NASA developed a spray can foam-in-place ablative material to repair damaged or lost TPS tiles. The hardware was never carried on the orbiter because of NASA’s confidence that the TPS would perform effectively, but it could be used to repair damage from meteoroids or debris on the TPS. Repairs to other orbiter elements might also be possible, although effective repair of the RCC leading edges would be very difficult because the repairs would have to survive exposure to very high temperatures during reentry.

NASA’s guideline that sets the maximum allowable risk of sustaining a critical penetration during a given mission suggests that one or two critical penetrations will occur during the 400 mission life cycle of the orbiter fleet (as of September 1997, 87 shuttle missions have been flown). In deciding how to allocate the finite resources of dollars, crew training time, and on-orbit operations time, NASA must determine whether in-orbit detection and repair of penetrations by meteoroids and debris outside the pressurized compartments are feasible and worthwhile.

The planned modifications to the payload bay door radiators and to the wing leading edge insulation appear to be positive steps that will have minimal negative effects on the overall program. NASA estimates that the modification to the

Front Matter (R1-R12)

Executive Summary (1-3)

1 Introduction (4-6)

2 Risk to the Orbiter and Crew (7-18)

3 Risk Management Strategy (19-26)

4 Tools for Risk Assessment (27-35)

5 Collision Avoidance (36-41)

6 Risk Mitigation (42-50)

Acronyms (51-52)

Appendix A: Statement of Task (53-55)

Appendix B: Biographical Sketches of Committee Members (56-58)